Debt - Components of the Convertible Notes (Details) - USD ($)	Jan. 25, 2020	Jan. 26, 2019	Sep. 15, 2015
Estimate of Fair Value Measurement
Debt Instrument [Line Items]
Debt instrument, face amount	$ 447,350,000	$ 467,104,000
Less: Debt discount and debt issuance costs	(37,474,000)	(61,801,000)
Net carrying amount of Notes	409,876,000	405,303,000
0.75% Convertible Senior Notes Due 2021
Debt Instrument [Line Items]
Debt instrument, face amount	460,000,000.0	485,000,000	$ 485,000,000.0
Less: Debt discount	(33,744,000)	(55,795,000)
Less: Debt issuance costs	(3,730,000)	(6,006,000)
Net carrying amount of Notes	$ 422,526,000	$ 423,199,000

Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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Face (par) amount of debt instrument at time of issuance.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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